The present invention relates to high molecular weight aliphatic polycarbonates and a process for their manufacture.
A process for the production of high molecular weight aliphatic polycarbonates is disclosed. The process entails a first stage wherein a low molecular weight aliphatic polycarbonate is prepared and a second stage where the low molecular weight aliphatic polycarbonate is condensed with diaryl carbonate in a melt transesterification process to form a high molecular weight aliphatic polycarbonate. The resulting high molecular weight aliphatic polycarbonate is suitable for the production of extrudates, films and molded articles.
The production of low molecular weight diol-terminated aliphatic polycarbonates on an industrial scale as feedstocks for the production of polyurethanes is known.
Thus, the production of low molecular weight diol-terminated aliphatic polycarbonates in homogeneous phase from chlorinated carbonic acid esters and aliphatic diols is described for example in DE 2 447 349 A. The production of such polycarbonates in the phase boundary process from chlorinated carbonic acid esters and aliphatic diols is described for example in DE 2 446 107 A. In addition DE 2 523 352 A, DE 2 546 534 A and DE 10 027 907 A1 for example describe the production of such polycarbonates in a transesterification process from carbonic acid esters and aliphatic diols.
All these processes have in common the feature that the maximum weight-average molecular weights Mw of the polymers are 15,000 to 20,000 g molxe2x88x921. Preferred molecular weights for industrial use as feedstocks in the production of polyurethanes are between 350 and 3000 g molexe2x88x921.
Further reaction of the low molecular weight polycarbonate polymers that can be obtained in this way to form high molecular weight, purely aliphatic polycarbonates has not hitherto been described, although it would be very useful on account of the considerably more favorable cost structure due to the use of cheaper monomers to replace aromatic high molecular weight polycarbonates by corresponding aliphatic raw materials.
High molecular weight polycarbonates with aliphatic polycarbonate blocks have up to now been described only in a few special cases. For example, EP 000 060 A1 describes the production of high molecular weight polyether co-polycarbonates. In this case low molecular weight polyalkylene oxide diols are converted to bischlorocarbonic acid monoaryl esters extended via carbonate groups. These are reacted further with bisphenols to form polyalkylene oxide diol bis-diphenol carbonates extended via carbonate groups, which are then condensed in the phase boundary process with phosgene and bisphenols to form polyether polycarbonates. Polymers with maximum mean molecular weights of 250,000 g molexe2x88x921 are obtained by this complicated three-stage process. A disadvantage is the fact that the aliphatic starting compounds are restricted to polyalkylene oxide diols. Furthermore it is not possible to produce high molecular weight, purely aliphatic polycarbonates in this way.
U.S. Pat. No. 3,161,615 described the production of high molecular weight 1,6-hexanediol copolycarbonates. In a first step a low molecular weight 1,6-hexanediol polycarbonate is formed by reacting 1,6-hexanediol with phosgene in pyridine, the resultant polycarbonate then being reacted further with bisphenol A and phosgene. However, it is not possible to produce high molecular weight, purely aliphatic polycarbonates in this way either.
A disadvantage in both these cases is furthermore the fact that the use of phosgene for industrial reaction purposes is difficult and complicated having regard to the considerable safety risks and high material costs due to corrosion.
DE 1 031 512 describes the production of high molecular weight aliphatic polycarbonates. In order for the reaction of for example 1,6-hexanediol and diethyl carbonate under alkali catalysis to yield high molecular weight aliphatic polycarbonates, a base-binding substance such as for example phenyl chloroformate must be added to the reaction in the oligomer range. A disadvantage has proved to be the fact that, after the neutralization of the catalyst, the transesterification can be continued only to a limited extent. From the applicants"" own experiments it is known that the achievable molecular weight is limited to approximately 28,000 g molexe2x88x921. However, the polymers have useful viscoplastic properties only above this molecular weight. Moreover, the production of mixed aliphatic polycarbonates according to this process is not described.
The production of high molecular weight linear aliphatic polycarbonates from cyclic aliphatic carbonates is described in EP 0 236 862 A2. Cyclic aliphatic carbonates are polymerized in a ring-opening solution polymerization with organometallic catalysts, such as for example butyllithium, in the presence of aprotic organic solvents to form polycarbonates. Polymers with molecular weights of up to 120,000 g molexe2x88x921 can be obtained in this way. A disadvantage with relatively large-scale batch production is that this process has to be carried out by an exothermic polymerization under the absolute exclusion of atmospheric oxygen and moisture and at temperatures of xe2x88x9250xc2x0 to 0xc2x0 C. The range of commercially available cyclic aliphatic carbonates is however limited to a few special compounds such as for example ethylene carbonate, propylene carbonate and neopentyl glycol carbonate. A production of mixed aliphatic polycarbonates is not possible according to this process.
Against the background of the prior art the problem therefore exists of providing an uncomplicated process for the production of high molecular weight aliphatic polycarbonates containing aliphatic polycarbonate blocks that is suitable for a large number of various aliphatic diols as starting materials and at the same time offers the possibility of producing mixed high molecular weight aliphatic polycarbonates.
This object has surprisingly been solved by the two-stage production process according to the invention.